Exclusion chromatographic separation of ionic from nonionic solutes

ABSTRACT

A process for effectively and economically separating an ionic component such as acid from a nonionic component such as sugar in polar solutions using ion exclusion technology whereby the viability of using hydrolysis to convert wood and agricultural waste products such as corn stover into fuel alcohol is substantially effected. Underlying the gist of this invention are newly discovered methods by which dispersion, caused by shrinkage of resin within ion exclusion columns, is controlled resulting in operation of such columns, over a wide range of process conditions to produce separate and distinct elution profiles for the acid and sugar. Successful operation of these new ion exclusion methods, techniques, and systems can replace lime precipitation which currently is being used in acid hydrolysis processing. This not only obviates the need for the large quantities of acid and lime required therein, but also eliminates the unwanted and highly ecologically undesirable production of huge quantities of waste gypsum.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment to us ofany royalty therefor.

This application is a division of application Ser. No. 08/382,450, filedFeb. 2, 1995, now U.S. Pat. No. 5,560,827.

INTRODUCTION

The present invention relates to substantial improvements in the area ofutilizing ion exclusion resins to separate into its components asolution comprising ionic and nonionic components and including, forexample, a solution comprising acid and sugar. For the purpose of theinstant invention, hydrolyzates, or acid and sugar mixtures produced bythe hydrolysis of a cellulosic material in the presence of an acidcatalyst, and acid/sugar mixtures or synthetic mixtures produced bysimple mixing in the laboratory, are referred to interchangeably. Moreparticularly, the present invention comprises a discovery by which thepreviously observed problem, normally associated with ion exclusion andgenerally referred to as dispersion; which dispersion is attributed toshrinkage of the resin, is substantially eliminated by employing a new,different, distinct, and substantially effective technique which rendersion exclusion a viable processing technique for separating ionic andnonionic components in a solution, including acid/sugar mixtures orhydrolyzates, one from the other, on a commercial scale. As used hereinresin in the "shrunken state" or just "shrunken" means and refers to astate in which, for example, a cross linked polystyrene, comprising thestructure of the resin and having a SO₃ ⁻ H⁺ functionality, contracts inthe presence of similarly charged ions in the process fluid due to theforce of repulsion. As used herein "resin in the swollen state" or just"swollen" or "swelled" means and refers to a state in which the crosslinked polymer, for example, polystyrene, comprising the structure ofthe resin and having a SO₃ ⁻ H⁺ functionality, expands to its fullyrelaxed state in the presence of a nonionic media which thoroughlypenetrates the micropore structure of the resin. As used herein,dispersion means and refers to a broadening and flattening of thechromatogram elution profiles. The term "band broadening" is also usedin chromatography to define this phenomenon, but this term will not berelied upon herein. Dispersion results from a variety of operatingconditions including shrinkage, supra, which often results fromintroduction of an acidic solution into a column containing an exclusionresin bed therein and thereby effects a continuous change inconcentration of the acid/sugar mixture above the resin bed. Theresulting dilution of the mixture, in turn, results in an undesirableoverlapping of the acid (ionic component) elution and sugar (nonioniccomponent) elution streams from such resin bed. By eliminating orproperly compensating for shrinkage, the resin, which acts as a sorbentin the process, effectively accelerates the elution of acid while at thesame time retards the progress of the sugar through the column therebypermitting complete, reproducible, and predictable separation of theacid/sugar mixture. The separation is effected by the difference in therelative sorption strengths. Strong electrolytes, such as sulfuric acid,are mostly or completely excluded from ion exclusion type resins by theDonnan effect (F. Helfferich, Ion Exchange, McGraw-Hill Book Company,New York, 1962), and appear first in the discharge from the column.Nonelectrolytes, such as sugar molecules in aqueous solutions, arereadily sorbed by such resins and, therefore, appear later in thedischarge from the column. It has now been found that practice of theinstant invention allows for continuous and protracted use of ionexclusion resin columns in large-scale or commercial-scale operationswhereas heretofore, the only effective technique available to prior artpractitioners for avoiding the deleterious effects of resin shrinkagewas to use only relatively small charges of acid/sugar mixtures to thecolumn, to thereby assure that elution of the separated constituents waseffected before significant resin shrinkage occurred along with theresulting undesirable and deleterious effects thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

As is well known, electrolytes can be separated from nonelectrolytes insolution therewith using any of a number of chromatographic techniquesincluding: ion exchange, ion exclusion, and ion retardation. Ionexchange systems, in which ions are exchanged between the solute and theresin bed, have found wide application in industry due mostly to thesystems ability to handle relatively high flux rates and a plethora ofionic species. However, because ion exchange does take place,regeneration of the resin is required. Ion exchange resins are typicallyclassified as strongly or weakly acidic or strongly or weakly basic.Strongly acidic resins usually contain sulfonic acid groups, whereasweakly acid resins usually contain carboxylic acid groups. Stronglybasic resins usually have quaternary ammonium groups while weakly basicresins usually contain polyamine groups.

An ion exchange resin with interchangeable Na⁺ ions is said to be in itssodium form. Introducing an electrolyte such as an aqueous solution ofH₂ SO₄ to the system results in an exchange of the Na⁺ with H⁺ ions andconvert the resin to its hydrogen form resulting in an elution of Na⁺from the column. The subsequent elution of H⁺ ions from the column,commonly known as "breakthrough," indicates that the column resin hasbeen mostly or fully spent. As may be appreciated, prior to the additionof more acid, such spent resin must be regenerated to its sodium form.

Ion exclusion systems, sometimes referred to as electrolyte exclusionsystems, employ the same resins used in ion exchange systems, discussedsupra, but differ in that the ionic functionality of the resin is thesame as that of the electrolyte and, therefore, there is no exchange ofions. As will be appreciated, resins used in the instant invention aretypically sulfonated polystyrenes with some degree of divinylbenzene(DVB) cross-linking which imparts physical stability to the resinpolymer. The sulfonic acid functionality of the resin particles causesswelling in aqueous media. The resulting microporous resin particles cansorb water and nonionic solutes. The degree of molecular cross-linkingwith DVB influences the extent of sorption and prevents totaldissolution of the porous resin. Because of ion repulsion and a highfixed acid chemical potential inside the resin microstructure, anelectrolytic species, such as sulfuric acid in an acid/sugar mixture,for example, is effectively prevented from entering the porous resin.However, the nonionic sugar molecules are free to diffuse into the resinstructure. Thus, electrolytes will pass through a packed resin bedfaster than nonelectrolytes which are held up or delayed within theresin's microporous structure. In applying the instant invention toeffect an acid separation similar to the separation used in the acidexchange system, supra, the resin used would be in its hydrogen form asopposed to the sodium form and, therefore, no ion exchange would occurin the system.

At the present time, ion exclusion technology is used for separation ofionic from nonionic or strongly ionic from weakly ionic solutes in polarmedia in certain analytical procedures, glycerin purification, and mixedacids separations applications (R. W. Wheaton and W. C. Bauman, AnnalsNew York Academy of Sciences, 1953, Vol. 53, pp. 159-176). It differsfrom conventional ion exchange in that there is no net ion exchangebetween solute and resin. This eliminates the need for resinregeneration. Ion exclusion technology appears to have utility inseparating ionic from nonionic species in aqueous solutions (D. W.Simpson and R. M. Wheaton, Chemical Engineering Progress, 1954, Vol. 50,No. 1, pp. 45-49). Basically, the ionic species are excluded from thefluid within the resin because of ionic repulsion within the resinparticle micropore structure. This phenomena is explained by the Donnanexclusion principle, supra. Contrastingly, the nonionic species have noionic repulsion with the resin and, therefore, penetrate the fluidwithin the porous resin to a greater degree. Thus, when a mixture ofthese two species is passed through a column of ion-exchange resin, theionic component elutes first because it is excluded from the resinstructure micropore volume. The nonionic species elutes after the ioniccomponent because it has penetrated the resin micropore volume.

The physical and chemical characteristics of the resin are of vitalimportance to the design of an ion exclusion process. The total resinpacked column volume can be thought of as to consist of three primaryzones: 1) the macropore, also called void or interstitial volume, V_(o),which is the liquid volume between the resin particles, 2) the microporevolume, also known as occluded volume, V_(p), which is the liquid volumeheld within the resin particles, and 3) the solid resin network volume,V_(r), which is the actual structure of the resin (S. R. Nanguneri andR. D. Hester, Separation Sci. & Tech., 1990, Vol. 25, pp. 1829-1842).Due to the inherent ionic nature of the resin, an unequal distributionof ionic solute species exists between the micropore fluid (inside theresin) and macropore fluid (outside the resin) fluid phases. Thus,different resins with different pore volumes, ionic functionalities, andionic charge density exhibit different separation characteristics withdifferent solutes.

Ionic species which do not penetrate or slightly penetrate into theresin micropore volume have distribution coefficients close to zero.Nonionic species which can penetrate the resin micropore volume havedistribution coefficients greater than zero but less than one. If achemical affinity exists between a species and the resin, then thedistribution coefficient can exceed one.

2. Description of the Prior Art

Ion exclusion, though widely used in analytical and pharmaceuticalapplications for many years, was not considered until recently for usein other than such applications due to the relatively low flux rates,small feed volumes, and weak electrolyte concentrations required tominimize dispersion and, thereby, provide for good species separation ofthe feedstock solution. Also, exacerbating the deleterious effects ofdispersion caused by high flux rates, large feed volumes, and strongelectrolyte concentrations was the dispersion caused by the presence ofa so-called dead volume above the resin bed. Such dead volume resultedfrom shrinkage of the resin bed caused by the presence of a strongelectrolyte such as sulfuric acid. Although identified as the primaryfactor contributing to dispersion, no successful means was devised untilthe discovery comprising the copending application of Hester et al.,Ser. No. 08/128,174, filed, Sep. 29, 1993, to deal with this phenomenonof dead volume caused by resin shrinkage. For purposes of teaching,disclosing, and claiming the instant invention, the teachings,disclosure, and claims of said reference, supra, to wit, Hester et al.,are herewith and hereby incorporated herein by reference thereto.

The possibility of using strongly acidic cation exchange resins for theseparation and recycle of acid from synthetic solutions of glucose andsulfuric acid has been investigated (R. P. Neuman et al., ReactivePolymers, 1987, Vol. 5, pp. 55-61). The work conducted at that timeusing Rohm and Hass Amberlite IR-118 resin in the hydrogen form andusing small columns demonstrated the potential for this type of processchromatography. Note: Any reference made herein to materials and/orapparatus which are identified by means of trademarks, trade names,etc., are included solely for the convenience of the reader and are notintended as, or to be construed, an endorsement of said materials and/orapparatus. Although no actual hydrolyzates were used in the workreported by Neuman et al., the synthetic solution containing 7.7 percentH₂ SO₄ and 1.0 percent glucose showed separation of glucose fromsulfuric acid at sample loading of 10 percent of the interstitial(column void) volume and at temperatures of 55° C. and 68° C. However,as noted by the authors, this work confirmed the potential forsignificant dispersion when operating even small ion exclusion systems.

The techniques revealed in the invention described and taught in thecopending application of Hester et al., supra, readily lend themselvesto batch applications, whereas the techniques revealed in the teachingsof the instant invention are directed primarily to practice insemi-continuous or continuous applications, such as simulated moving bed(SMB) technology. SMB systems such as the Shanks merry-go-round havebeen applied in adsorption and ion exchange systems for many years. TheShanks system for leaching soda ash was introduced in England in 1841.The use of SMB or merry-go-round systems is quite common in thepharmaceutical industry as described in: (J. W. Chen et al., Ind. Eng.Chem. Process Des. Devel., 1972, Vol. 11, p. 430); for activated carbonadsorption in the chemical industry (H. J. Fornwalt and R. A. Hutchins,Chem. Eng., May 9, 1966, Vol. 73, No. 10, pp. 155-160) and (M. J.Humenick, Jr., "Water and Wastewater Treatment," Calculations forChemical and Physical Processes, Marcel Dekker, New York, chap. 6,1977); for ion exchange in uranium purification (M. Streat, J. Sep.Process Technol., 1980, Vol. 1, No. 3, p. 10); and for waste watertreatment with activated carbon (R. L. Culp et al., Handbook of AdvancedWastewater Treatment, 2nd ed., Van Nostrand-Reinhold, New York, chap. 6,1978), and (C. T. Lawson and J. A. Fisher, AIChE Symp. Ser., 1974, Vol.70, No. 136, p. 577), and (J. D. Parkhurst et al., Water Pollut. ControlFed. J., 1967, Vol. 39, No. 10, Part 2, pp. R70-R80). The primaryadvantages of SMB or similar systems in ion exclusion are the lowerrequirements (i.e., reductions of greater than 50 percent) for amountsof resin, water, and energy.

In work conducted at a time prior to the making of the instantinvention, new methods and means were quite unexpectedly discovered toovercome or compensate for the deleterious effects of dispersion, whichnew methods and means much more efficiently utilized ion exclusiontechnology to separate ionic components from nonionic components insolution than were taught in the art prior thereto. This most recentadvance in the prior art is discussed and claimed in greater detail inHester et al., supra. Hester et al. teach utilizing a standard columnor, more preferably, a combination of several columns operated in serieshydraulic order which columns are adapted with a specially designedfixed or, more preferably, a specially designed movable or floating headdistribution plate to effectively eliminate dispersion normallyresulting from dead volume effected by the shrinkage of the ionexclusion resin when exposed to strong electrolytes such as sulfuricacid. In a principal embodiment envisioned by Hester et al. one or morecolumns of ion exchange resin, converted to its hydrogen form, hence ionexclusion resin, are subjected to repeated introduction at or into theuppermost regions thereof of hydrolyzate, nominally aqueous mixtures ofsugar and sulfuric acid, followed by water washing, wherein separationtherebetween is effected by the elution of the ionic component ahead ofand completely apart from the nonionic component. In a convenientdepiction thereof each column, in the case of a series of columns beingutilized, is subjected to introduction of both the hydrolyzate and thewash water through introduction of same into or near the top of thefloating head assembly and onto the upper surface of the resin bedfollowed by elution of the separated components at or near the bottom ofthe column. As taught in this most recent prior art, the force ofgravity may be utilized to effect juxtaposition of the bottom surface ofthe floating head with the top or upper region of the resin bed so thatas said resin bed shrinks, the so-called floating head is urged to stayin continual contact or close proximity therewith. For convenience, insaid invention the preferred embodiment described introduction of thehydrolyzate and the wash water through the floating head and onto thetop of the resin bed. This arrangement proved to be generally desirablein that it provided a readily useful method and means for effectingdistribution in a more or less uniform manner of the input liquid ontothe top of the resin bed. Also referenced in the copending applicationof Hester et al. is the teaching of utilizing a plurality of suchcolumns in an arrangement known in the art as a simulated moving bed.For those who are not comfortably familiar with the art relating tolarge-scale or commercial-scale adsorption and chromatographyapplications, attention is directed to Large-Scale Adsorption andChromatography, Volume II, Phillip C. Wankat, Ph.D., CRC Press, Inc.Boca Raton, Fla. 1986.

SUMMARY OF THE INVENTION

In one of the principal embodiments for effective practice of theinstant invention, a plurality of ion exclusion columns are convenientlyarranged and grouped into four zones in a manner like those shown inFIG. 6-10B of Wankat, supra, except that instead of moving the resin bedparticles, the movement thereof is simulated in the manner and withmeans similar to that shown in FIG. 6-29 of Wankat, supra. In thearrangement and system utilized for explanation of this preferredembodiment of the instant invention, only one column or section isutilized per zone, it being understood, of course, that the resultingoversimplification is necessary for a clear understanding of thedisclosure, but that in actual operation, a plurality of columns will beutilized for at least each of zones I and III. During operation of thesystem and practice of the instant invention, the fluid connectionsinterfacing the input and the output of materials into and out of saidzones together with the flow connections established and redirected viamanifolds between said zones will be in a manner such that the feedstreams for hydrolyzate and wash water and the collector receptacles foroutput of separated components remain stationary as do the individualion exclusion columns, but, nevertheless the flow paths are directed andredirected via ports or valves therebetween in a sequenced manner so asto simulate a moving bed of ion exclusion resin. Accordingly, it will beappreciated that in the practice of the instant invention four zones areestablished in the manner and with the means shown in and describedlater in greater detail in the discussion of FIG. 1. For purposes ofsimplicity and ease of understanding, the description herein is directedto an arrangement wherein each zone comprises but a single column.

As has been previously noted, the instant, new, and novel invention maybe used in substitution for either or both the floating head and thefixed head embodiments, first taught and claimed in Hester et al.,supra. Nevertheless, it is anticipated that at least some of thebeneficial effects of the floating head embodiment may conveniently andexpeditiously be combined with those of the instant invention, whenconsideration is given to the fact that although practice of the instantinvention eliminates any dead volume, at the entry point or interfacejuxtaposed feedstream entry into the column, the overall movement orshifting of the mass column during subsequent shrinkage gives rise to aregion at the top of the column, wherein only eluded solutions sansresin particles are found. Accordingly, in order to prevent mixing ofthe eluded solutions in this upper area of the column, a movablecollection device which can maintain juxtaposition with the resinparticles at the top of the bed has now been found to effectivelyremediate the problem.

To the uninitiated, it might appear that the direction of flow throughthe column from either top to bottom or bottom to top is of littleconsequence since the force of gravity will act on the mass of thecolumn to keep the resin particles comprising same juxtaposed the bottomzone and the floating head will maintain juxtaposition of its bottomsurface with those resin particles comprising the top of the column.Contrary to this postulated conclusion, it has now been found that,indeed, in the unique combination now herein under consideration,superior results will be attained when the flow is upwardly directedthrough the column. Although this unexpected difference in performanceof these two arrangements is not completely understood, it is believedthat perhaps one of the more significant contributing factors thereto isthat the deleterious effects attributable to channelization of fluidflow through the resin bed is more effectively countered when the bedparticles are shifting downwardly to take up the slack for shrinkage ofparticles therebelow than is the case when particle shrinkage occurs ina direction from top-to-bottom of the bed as in Hester, supra. If thisunexpected further improved resulting performance is indeed attributableto correction of the resin bed for resulting channelization, then itbecomes an even more significant factor when the instant invention andsystem is operated on a continuous basis, as herein contemplated, sinceconventional use of externally induced mechanical means or stirringtends to interrupt such continuous operation.

OBJECTS OF THE INVENTION

It is therefore a principal object of the present invention to developefficient and economical commercial-scale systems for separatingelectrolytes from nonelectrolytes or strong electrolytes from weakelectrolytes in mixtures or hydrolyzates comprised, for instance, ofacid and sugar by using a chromatographic method heretofore consideredviable only for analytical applications or wherein sharp separations ofspecies are not required.

Another principal object of the present invention is to develop achromatographic system which minimizes the use of a displacing fluid,such as water, to force a hydrolyzate through a series of resin beds tothereby reduce dilution of product streams with such displacing fluid.

Still further and more general objects and advantages of the presentinvention will appear from the more detailed description set forth inthe following disclosure and examples, it being understood, however,that this more detailed description is given by way of illustration andexplanation only and not necessarily by way of limitation, since variouschanges therein may be made by those skilled in the art withoutdeparting from the true scope and intent of the instant invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from a consideration ofthe following description taken in connection with the accompanyingdrawings in which:

FIG. 1 represents one embodiment, in time slice mode, of the instantinvention, wherein at time equal zero (in arbitrary dimension), atypical SMB arrangement is utilized in a new combination with ionexclusion resin, said resin being in its hydrogen form, and furthercombined with the most preferred embodiment of the instant invention,wherein flow of solution past the particles comprising the resin bed ineach column is purposely directed in an upward direction to therebysubstantially eliminate the necessity of employing a moveable feederassembly to overcome, at the inlet end of each column, the deleteriouseffects of dispersion, which feeder assembly may be constructed in amanner similar to the floating head which is the subject of the priorfiled, copending application of Hester et al., supra, it beingunderstood; however, that, if desired, the instant invention may bepracticed in a manner wherein both such upward flow and a modifiedversion of such floating head design are combined in an alternative mostpreferred hybrid embodiment, albeit, the resulting moveable collectorassembly or modified floating head device is not shown due to the greatplethora of other means required for understanding of the port switchingsequencing necessary for practice of the instant invention. Althoughdiscussed in greater detail below, it will become apparent to the readerthat operation of the instant system incorporates a valve (or, asoftentimes herein used interchangeably therewith, port) switchingsequence wherein simulation of the moving bed is in a direction suchthat zones appear to move from left to right and thereby to more closelyapproximate some of the prior art discussions of Wanket, supra.Nevertheless, it should be appreciated that the sequencing could beoperated in another manner wherein the resulting simulation of a movingbed would be in the opposite direction.

FIGS. 1-5 represent both the original time slice or sequence and thefour subsequent port switching sequences necessary to simulate a totallooping of the columns back to the original position arbitrarilyselected for the depiction comprising FIG. 1, supra.

Because an understanding of the valve sequencing for simulating movementof the bed from the point of view for an observer fixed on the ground,wherein he or she sees a stationary solid with valves changing thelocation of product and feed ports; therein is also included in each ofthe respective FIGS. 1-5 an indication of which inlet valves are openfor feed of hydrolyzate and wash water from the input manifolds, andwhich outlet valves are open for directing recovered eluded streams ofionic and nonionic separated species to the collection manifold, both ofsaid showings being by means of the respective valves being enclosed ina circle.

FIG. 6 represents one embodiment of the instant invention incross-sectional, side-elevational view, taken along a line perpendicularto the longitudinal axis of any of the many resin columns employed inour system, with said line in a plane parallel to and coincident withsaid axis, wherein is depicted a movable fluid collecting assembly usedto prevent principally cross-over contamination from the top dischargeend of the column, particularly during the transition between cessationof ionic species elution and initiation of nonionic species solution.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now specifically to FIG. 1, in the depiction shown therein, itwill be noted that the four zones, to wit, I, II, III, and IV coincide,respectively, with outlet valves 101, 102, 103, and 104. Said outletvalves are shown as feeding the ionic outlet stream represented hereinsimply by line 120, which in the case of sugar-acid hydrolyzate willrepresent the acid recovery manifold. It will, of course, be appreciatedthat the flow of materials from zone I, II, III, and IV to and/orthrough said outlet valves 101, 102, 103, and 104 is through lines 121,122, 123, and 124, respectively. In like manner, the collection manifoldfor the ionic species is simply represented via line 130, which is fedfrom zone I via line 131 and outlet valve 105; from zone II via line 132and outlet valve 106; from zone III via line 133 and outlet valve 107;and, from zone IV via line 134 and outlet valve 108.

On the feed end of the system shown herein, it will be appreciated thata hydrolyzate feed stream may be introduced via manifold means hereinrepresented simply as line 140 wherefrom via inlet valve 113 and line141 same can be introduced into zone I. In like manner, hydrolyzate feedstream can be introduced from manifold 140 via inlet valve 114 and line142 to zone II, via inlet valve 115 and line 143 to zone III, and viainlet valve 116 and line 144 to zone IV. Also, displacing fluid, i.e.,in the case of an acid/sugar mixture, wash water, may be introducedthrough the input manifold means which is simply represented as line150, wherefrom via inlet valve 109 and line 151 it may be introducedinto zone I, via inlet valve 110 and line 152 it may be introduced intozone II, via inlet valve 111 and line 153 it may be introduced into zoneIII, and via inlet valve 112 and line 154 it may be introduced into zoneIV.

In this first time slice, the valves have been switched in a mannerwherein outlet valves 101 and 107, and inlet valves 113 and 111 are openand the remaining outlet and inlet valves, respectively, are closed.Accordingly, hydrolyzate is flowing to the inlet of zone 1 while theionic species, separated at the opposite and outlet end thereof, isflowing through outlet valve 101. Simultaneously therewith, makeup washwater is being introduced into the inlet of zone III through inlet valve111 and the nonionic species eluded from the other end thereof is beingcollected in manifold 130 through outlet valve 107. It will, of course,also be appreciated that simulated moving bed exchange systems of thetype herein described require considerable desorbent, in this case, washwater. It is estimated that 10 to 20 weight percent units of wash waterwill be required to remove a single weight unit of sugar; therefore, thesystem must be provided with recycle means herein depicted as recyclelines 161-164 feeding recycle to zones I-IV, respectively.

For the arrangement shown herein, it will be understood that for zonesII and IV, none of the inlet and outlet valves are open. For zone I,inlet valve 113 and outlet valve 101 are open and for zone III inletvalve 111 and outlet valve 107 are open. For ease of understanding andto facilitate more readily perceptual appreciation of this time sliceand those shown and described in greater detail, infra, the open inletand outlet valves are depicted enclosed in a bold line circle. Morespecifically, the circle enclosing open inlet hydrolyzate valve 113 isidentified as 171. Likewise, the circle which encloses open displacingfluid inlet valve 111 is identified as 172. The circle which enclosesopen acid outlet valve 101 is identified as 173, and the circle whichencloses open sugar outlet valve 107 is identified as 174. All othervalves are in the closed position.

Referring now more specifically to FIG. 2, therein is shown thearrangement of the instant system subsequent to switching the valvearrangement depicted in FIG. 1 to that shown herein, wherein the inletvalves from the hydrolyzate and wash water manifolds which have now beenswitched to their open position are 116 and 110, respectively, andwherein the outlet valves for controlling flow to the ionic and nonioniceluded species to the respective manifolds are 104 and 106,respectively. Accordingly, it will be appreciated that as between thearrangement shown in FIG. 1, supra, at dimensionless time zero and thearrangement shown herein in FIG. 2 at an increment of dimensionless timesubsequent thereto and after the first sequence of valve switching hasbeen effected the simulation of the moving bed has the effect that thecolumn which was zone IV in FIG. 1, is now herein FIG. 2 zone I andlikewise the column which was zone I in FIG. 1, now herein FIG. 2becomes zone II, the column which was zone II in FIG. 1 herein FIG. 2becomes zone III, and the column which was zone III in FIG. 1 hereinFIG. 2 becomes zone IV.

For the arrangement shown, it will again be appreciated that for zonesII and IV none of the inlet valves are open. For zone I, acid inletvalve 116 and acid outlet valve 104 are open, and for zone III, waterinlet valve 110 and sugar outlet valve 106 are open. Again, as in FIG.1, herein FIG. 2 the open or activated inlet and outlet valves, supra,are shown enclosed in the respective circles referenced in thediscussion, supra.

Referring now more specifically to FIGS. 3-5, therein are representedsuccessive and subsequent sequenced stepping of valve switching similarto that described in FIG. 2, supra, wherein it may be seen that onceagain no inlet or outlet valves are open at the column, or group ofcolumns, which represent either zones II or IV, that the sequencing ofvalve switching continues from and includes steps through valve 116,115, 114, and finally back to 113. Likewise, starting with thearrangement shown in FIG. 2, the inlet wash water valve steppingsequences from that shown at 110 to 109, thence to 112, and finally backto 111 for zone III as it originally was shown in FIG. 1. As far asoutlet valves to the ionic and nonionic manifold species represented byline 120 and 130, respectively, the total sequence starting with FIG. 1and ending back with the same arrangement shown therein in FIG. 5 stepsthrough respectively outlet valves 101, 104, 103, 102, and back to 101.Likewise, the valve stepping for the nonionic species outlet orcollection manifold feed, with the arrangement shown in FIG. 1, stepsthrough sequentially outlet valves 107, 106, 105, 108, and finally backagain to 107.

Referring again to FIGS. 1-3, supra, it will be appreciated by thoseskilled in the art that more complete separation can be achieved byadding additional resin columns to at least some of the zones. Forinstance, all of the nonionic component, such as sugar, must be eludedfrom zone III in FIG. 1 before the first stepping to effect the valveswitching for the arrangement shown in FIG. 2, else at least somenonionic species can be carried into zone IV in the arrangement of FIG.2, and thence eventually into zone I in the arrangement or time slicerepresented in FIG. 3, whereby that portion of said nonionic specieswill inadvertently be released through open outlet valve 103 intomanifold 120 providing unwanted cross-contamination of the principallyionic species collected thereby. One solution to the problem ofachieving complete elution from the respective zones so there is nocarry forward or backward for cross-contamination between the recoveredspecies is to add additional columns to at least some of the zones.

Since it can be readily appreciated that as described, supra, themovement of the ionic species through the column is substantially andrelatively greater than the hold up of the nonionic species into and outof the plethora of resin particles for movement through the column andfurther in view of the theoretical mathematical model as proposed inconjunction with Wanket's FIG. 610B, on page 59, operation and practiceof the instant invention required that the relative movement of ionicspecies in zones I and II is in the same direction as the movement ofthe nonionic species in zone III, but opposite to the direction of thenonionic species in zones I and II. It will be appreciated that modelingwhich is principally directed to determining column size and number ofcolumns leads to the conclusion that the number of resin columns whichare to be utilized for separation and refluxing of nonionic species issubstantially greater than the number required for like effect on theionic species. With this in mind, it was determined through mathematicalmodeling that the number of columns which comprise zone I may preferablyrange from about 2-10 and most preferably may range from 3-9, whereasthe number of columns which comprise zone III preferably should rangefrom about 5-17 and most preferably be about 8-15.

Referring now specifically to FIG. 6, dilution or cross-contamination ofthe eluded streams caused by resin shrinkage in any column iseliminated, regardless of hydrolyzate feed conditions, by means and useof the instant movable collector assembly, generally illustrated at 601and generally comprising end cap 602, movable portion 603, and flexibleconduit 604. The density of the movable portion 603 of movable collectorassembly is, or can be adjusted so as to float atop the resin as theresin bed changes in volume due to exposure to different acidenvironments. Movable portion 603 of collector assembly device 601eliminates fluid dead volume above the resin bed comprised of a plethoraof individual beds, one of which is generally illustrated at 605, whichdead volume would otherwise contribute to cross-contamination in thepool of product which would normally be collected thereabove. Forinstance, fluid flowing up through the column, which column is generallyillustrated at 606, enters the bottom of movable portion 603 ofcollector device 601 conveniently through any of a number of apertures,one is conveniently shown as aperture 607, and thence through conduit604, part of which is shown within movable portion 603 of collectorassembly 601, and thence through the coil or flexible section of tubingthereabove, and finally out through the aperture in end cap 602, itbeing understood, of course, that movable portion 603 of collectorassembly 601 is of a cross-sectional area with the inside dimension ofthe column generally represented at 605. Also shown is sealing means 608which can be of any of many convenient designs for ensuring that asmovable portion 603 of collector assembly 601 shifts downward in column605, the eluent collected through any of apertures 607 is directedthrough conduit 604, rather than short circuiting around movable portion603. Although conduit 604 may most conveniently be a coiled or flexiblepiece of silicon or Teflon tubing, all that is really required is toprovide compensation means for changes in juxtaposition caused by therelative movement between end cap 602 and movable portion 603. Inaddition, it will also be appreciated that although end cap 602 helpsfacilitate operation of the instant collector assembly, it can bedispensed with or incorporated in a composite design of the type shownin FIG. 3 of Hester, supra. Also, the specific gravity of movableportion 603 of collector assembly 601 is preferably provided in a manneradjusted so that the effective weight thereof on the bed of resinparticles therebeneath is sufficient to maintain close juxtapositioningtherebetween. Alternatively, any of a number of physical drive meansshown or discussed in Hester, supra, may be utilized to maintain suchclose contact.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the teachings of the present invention, electrolytessuch as sulfuric acid can be efficiently recovered from nonelectrolytessuch as glucose through a procedure employing ion exclusion resins. Aprincipal embodiment of the instant invention utilizes a plurality ofcolumns in the manner of a simulated moving bed with introduction andflow of fluids therethrough in a manner to either completely orsubstantially compensate for the deleterious effects of dispersionattributable to the so-called "dead volume." In this new and improvedarrangement and technique there is no requirement to rely solely onfloating heads of the type described in the invention of Hester et al.,supra, to overcome the deleterious effects of dispersion at that end ofthe resin column wherein materials are introduced; however, as will bewell appreciated from a further reading of these teachings, a devicesimilar to such floating head may, if desired, be expeditiously employedas a moveable collecting assembly at the eluting end of the column toprevent unwanted or unintended mixing thereat of the elution streams,particularly during or near to the transition from output of elution ofone species to another, i.e., when, for example, the elution of theionic component is or nears completion and the elution of the nonioniccomponent is about to, or has commenced.

In the practice of the instant invention, a plurality of ion exchangecolumns may be used in either the traditional manner or further modifiedfor combination with use of the movable collector arrangement, supra. Ineither embodiment, the force of gravity is utilized to compensate forion exclusion resin shrinkage upon exposure of same to an acidenvironment without the use, at or near the input ends of such columns,of a movable assembly, because the flow into such columns is into thebottom regions thereof. As will be described and shown in greater detailinfra, the continuous solids flow fractionation system or as oftentimesreferenced, the moving bed system depicted on page 59 of Wankat, supra,can be simulated in a manner wherein the resin is not physically movedthrough the columns comprising the system, but rather a technique ofspecially arranged manifolds and valves is utilized with preselectedopening and closing of such valves to simulate resin movement throughthe system. More particularly, a further reading of the instantdisclosure will reveal to those skilled in the art that the SMBarrangement shown on page 82 of Wankat, supra, closely approximates thesimplest form of such a valving arrangement for practice of the instantinvention with, of course, appropriately predetermined timed sequencingof input and output stream flows.

It should, of course, be remembered that although reference herein ismade in a liberal manner to the disclosure and teachings of Wankat,supra, those prior art teachings are restricted to product separationswith resins in the sodium form thereby requiring replacement and/orrejuvenation see, for example, page 70 of Wankat, supra, whereas theinstant invention, which builds on the teachings and disclosures ofHester et al., supra, relies on and for the first time teaches methods,means, and techniques for employing such resins in their hydrogen form.This is important to remember since perhaps the most significantdeparture of the instant invention from that of Hester et al., supra, isthe reversal of flow through the columns from bottom to top, rather thantop to bottom. Although it may be argued that this flow reversal orcountercurrent flow of input into the columns is anticipated by FIG.6-29 on page 82 of Wankat, supra, it should be remembered that asignificant departure of the teachings of the instant invention fromthat of Wankat, supra, is that the separation in such a SMB treatment istaught by utilizing exchange resins in their hydrogen form, rather thanin their sodium form.

In addition, Wankat, supra, teaches that with his system all effortsshould be maintained for minimizing the deleterious effects ofdispersion and suggests in furtherance thereof that the columns bepacked with ion exchange, rather than ion exclusion resins, said resinsselected to be of the smallest diameter particle size practical. Such apractice of using small size resin particles, while increasing theeffective mass transfer area and, consequently, the number oftheoretical trays per unit length of column, does have drawbacks. Acolumn packed with smaller resin particles would be more likely tobecome occluded; therefore, only feed solutions essentially free of eventhe smallest particulates could be used. In addition, as described inNanguneri, S. R., "Design, Development and Analysis of a PreparativeScale Ion Exclusion Chromatography System," Ph.D Dissertation, theUniversity of Southern Mississippi, smaller resin particles exhibitdiminished separation properties since they tend to produce lowerdistribution coefficients. In the practice of one of the most preferredembodiments of the instant invention, exchange resins of relativelylarge size (50-100 mesh) having two percent DVB crosslinking versus therelatively small size (>400 mesh) recommended by Wankat, supra, producedexcellent resolution of the sugar and acid elution profiles. On theother hand, as further described in Nanguneri, supra, the lowerdistribution coefficients caused by the smaller size resins can beoffset by using resins containing lower levels of DVB crosslinking.However, the very small size recommended by Wankat, supra, would requireresins with little structural integrity and, therefore, could notwithstand the mechanical stresses exerted during normal expansion andshrinkage. It has now been found, quite unexpectedly, that the use ofsuch larger size resin particles even in view of Wankat's, supra,admonition regarding such large resin particle size is advisable in thepractice of the instant invention.

The upward flow in the columns in the instant invention causes theshrinking resin bed to be urged by gravity to remain in juxtapositionwith the bottom of the container forming each individual column, andfurther that, at least initially, the greatest degree of shrinkageoccurs in these bottom regions. Conveniently, the bottom of each of suchcontainer may be disposed in the manner of a solution sparger. As saidresin continues to shrink and the effects thereof are evidenced in everrising regions even further upward of such columns, it will beappreciated that the top of the column, once tightly packed with resinwill move downwardly which will ordinarily give rise to formation of apool of eluded solution thereover and that at the crossover point ofoperation wherein the ionic species has completely or substantiallyeluded and the nonionic species initiates elution, such resulting poolat the top of the column could give rise to an unwanted and undesirablemixing of the two now separated species. By providing a movablecollector assembly, similar to the floating head of Hester et al., whichfollows the top of the shrinking resin bed downwardly through the forceof gravity or with the aid of physical drive means, the size of the poolof eluded solution collected above the resin bed is minimized byremoving same through the modified movable collector assembly to thecollection manifolds. Accordingly, it should now be appreciated that theinstant invention, by using countercurrent or upward flow, relies on theforce of gravity rather than the prior art floating head to overcome thedeleterious effects of dispersion at the input end of each resin columnand relies on a new and novel movable collector at the output end ofeach column to prevent the resulting and otherwise efficient and veryeffective separation of species from remixing after they are eluded fromthe collecting end of the resin column.

As previously discussed, the phenomenon commonly referred to in the artas dispersion is effected, at least in part, from mechanical shrinkageof a packed resin column. In the practice of ion exclusion technology,resins which are suitable for use therein are delivered by themanufacturer in dry form and must be activated before being packed intosuch columns by exposure of same to aqueous media provided withrequisite H⁺ ions in concentrations sufficient to convert the resin toits hydrogen form. For example, the dry resin may be introduced into acontainer and mixed with sulfuric acid. Although not widely appreciatedby some researchers, the contact of such resins with the conversionmaterial such as sulfuric acid causes a relatively significant change ineffective volume by causing shrinkage of the individual resin particles.Subsequent to such conversion, however, the resin must be washed withhydrogen ion-free aqueous media as, for instance, water, to removeexcess H⁺ ions. Again, although not widely appreciated by someresearchers, the subsequent washing of the resin, now converted to thehydrogen ion form, causes a reversal of the change in volume whereby theindividual resin particles swell and thereby increase in size.Subsequently, the resulting washed and swollen resin is packed into thecolumn in a manner wherein no discontinuities or voids other than thosenormally attributable to packing volume are allowed. The relativechanges in volume, i.e., by either shrinkage or swelling can account forchanges in total resin volume equivalent to about 20 percent.

It will now be appreciated that when the resulting packed column isutilized for purposes of ion exclusion with a mixture such as acid andsugar as described in the prior art portions of the copendingapplication of Hester et al., the exposure of the resin particles to theacidic component therein will cause same to shrink, thereby effecting acontraction of the column packing and consequently effecting a so-calleddead volume at the uppermost portion thereof. It will also beappreciated as more of the acid/sugar mixture or hydrolyzate is added tothe column, such shrinkage will be effected ultimately throughout thelength of the column. Accordingly, the dead volume above the resinmaterial in the Hester arrangement will become a heel of acid/sugarfeedstock of ever changing size and concentration as the acid componenteither moves rapidly through the intricacies comprising the packingvolume throughout the column or is prevented from entering the resin bedbecause of the Donnan effect while the sugar molecules become defusedinto the resin microstructure. The net effect is to cause a volume ofever changing size and of ever changing mixture concentration in theheel interfaced with the top of the resin column so as to effectflattening and broadening of the elution profiles of both the acid andthe sugar components, whereby the desired good species separation asclean cuts of two eluent streams is not realized. For a more completeunderstanding of the significance of such dispersion, attention isdirected to Nanguneri, supra.

Practice of the instant invention through application of the new instantprocedures and techniques has been found to maximize the performance ofthe resin bed thereby permitting efficient operation of same atsignificantly higher feed volumes, flux rates, and electrolyteconcentrations than heretofore obtainable in standard ion bed systems.Therefore, by utilizing upward flow in the resin bed columns there iseliminated a so-called dead volume juxtaposed the inlet end of the resinbed without requiring the use of any movable mechanical aid such as thefloating head, supra, whereby it is possible to more accuratelymathematically model large-scale ion exclusion chromatography systemssince dispersion caused by high acid concentrations, high flux rates,and large feed volumes can be readily predicted. In addition, asdescribed herein, through the practice of the most preferred embodimentof the instant invention, it is possible to achieve even further andmore significant performance enhancement in the operation of ionexclusion chromatography systems. In this most preferred embodiment, itis possible to counter the effect of resin shrinkage which occurs whensaid resins are exposed to normal column cycling as described herein bycombining such upward flow with the use of a collection device movablewithin and complementary, in cross-section, to the portion of the resincolumns within which it is designed to operate.

It has now been discovered that the objectives of the instant inventioncan easily and effectively be attained by redirecting the flow of fluidsthrough the column so that movement thereof is in an upward, rather thanin the downward manner which is suggested by the teachings of Hester etal., supra. The net result of this innovation is to cause the resinparticles at the bottom of the column or container to initially becontacted with the most acidic hydrolyzate environment, rather than theparticles at the top of the column which is the case under theheretofore customary prescribed manner of operation. Accordingly, itwill be appreciated that the initial shrinkage of the resin particlestakes place in the bottom of the container, rather than at the top andthat the force of gravity acting on the plethora of particles comprisingthe bed therein simply, but very effectively forces the bed down to andin contact with the vessel bottom so that the deleterious effects of adead volume are minimized or precluded. As the acid constituent of thefeedstock initiates shrinkage of the resin particles, any would-be deadvolume thereunder is immediately filled by downward movement of the bed.Of course, as the resin particles are caused to further shrink andcontract in the bed, the mass of resin particles in the columneffectively moves downwardly to maintain the interface between itsbottommost portion and the bottom of the container, thereby ensuringthat no, or substantially no, dead volume is allowed to form at, orjuxtaposed said inlet interface from which the unwanted and undesiredresults of the phenomenon of dispersion can result. In short, theinstant new and novel embodiment prevents establishment of anysubstantial depth or thickness of an ever-changing concentration of anacid/sugar mixture between the bottom of the packed column and thebottom of the container forming the column.

INVENTION PARAMETERS

After sifting and winnowing through the data supra, as well as otherresults and operations of our new, novel, and improved technique,including materials and information incorporated herein by referencethereto, methods and means for the effecting thereof, the operatingvariables, including the acceptable and preferred conditions forcarrying out our invention are summarized below:

    ______________________________________                                                                            Most                                                      Operating  Preferred                                                                              Preferred                                 Variables       Limits     Limits   Limits                                    ______________________________________                                        Acid Concentration (% H.sub.2 SO.sub.4)                                                        1.0-20.0   3-17     5-15                                     Column Aspect Ratio                                                                           0.25-50    0.5-8.0  1.0-5.0                                   No. of Columns (Total)                                                                         5-50      10-35    15-30                                     Zone I           1-14       2-10    3-9                                       Zone II         1-9        2-5      3-4                                       Zone III         2-23       5-17     8-15                                     Zone IV*        1-4        1-3      1-2                                       Resin (% DVB cross-linking)                                                                    1.0-15.0   2.0-12.0                                                                              2.0-8.0                                   ______________________________________                                         *In the embodiment wherein the lower limit of number of columns is zero,      the system can be considered as being comprised of a three (3) zone,          rather than of four (4) zones.                                           

These parameters represent the principal parameters that must be kept inmind in predetermining or otherwise arriving at acceptable operation ofthose aspects of the instant invention pertaining to columnchromatography. A less obvious but equally important parameter is columnlength or, in the SMB system, aspect ratio, i.e., ratio of column lengthto column width/diameter. As described in Hester et al., supra,particularly as it applies to single column operation, an acceptablecolumn operation at higher feed volumes is possible with use of a longercolumn. In designing such a single column system, it is of utmostimportance to mathematically predict that column length required. On theother hand, for the application herein being considered, the effectivecolumn length needed to prevent a mixing of the elution streams is afactor of the length of the number of columns which are employed toeffect any particular zone. However, since the sugar or nonionic specieselution time is always greater than that of the ionic species thisconsideration is of the most importance in the system designarrangement. The use of the instant invention allows designers toaccurately predict, by means of readily available theoreticalcorrelations of the type set forth in Wankat, the operatingcharacteristics of any ion exclusion column chromatography systems byotherwise avoiding consideration of the less quantifiable phenomenacaused by the presence of a dilution layer both at the inlet end andoutlet end of the resin bed. Accordingly, the results of one such modelused to predict total column length and number of columns in each zone,as depicted infra, are summarized below. The results are for an IECsystem consisting of 10 centimeter diameter columns operating with thefollowing conditions: a feed of 100 grams per minute containing 7percent glucose and 7 percent sulfuric acid; a recycle flow rate, resinmacropore fluid flow rate, and resin micropore fluid flow rate of 290grams per minute, respectively; a water flow rate of 134 grams perminute; and 95 percent acid and sugar recovery efficiencies.Additionally, the height equivalent to a theoretical plate (HETP) foracid was estimated at 0.2 centimeters and the HETP for sugar wasestimated to be 4 centimeters, the sugar partition coefficient was setat 0.4 and the acid partition coefficient was set at 0.05. The partitioncoefficients as well as the HETP values were estimated from datacollected in tests described in Hester, et al., supra. The sugarconcentration in the recycle fluid entering zone IV, see page 59, ofWankat, supra, was set at 0.02 percent. Since the recycle flow wasassumed equal the macropore fluid flow, the sugar concentration at thetop plate is equal to the sugar concentration of the recycle fluid. Thegeneral formula used for the system model is:

    x.sub.n+1 =x.sub.n +(L*(x.sub.n -x.sub.n-1)/R*Ks+Q)

where

R=Resin micropore fluid flow, (gm/min)

Q=Resin macropore fluid flow, (gm/min)

x_(n) =Sugar concentration of the n^(th) tray, (percent)

L=Total of the input and output streams at the various zones, (gm/min)

Ks=Sugar distribution coefficient

    ______________________________________                                                       IEC System Design                                              ______________________________________                                        Individual column length                                                                        30 cm                                                       Columns in Zone I                                                                              8                                                            Columns in Zone II                                                                             3                                                            Columns in Zone III                                                                            11                                                           Columns in Zone IV                                                                             1                                                            Total number of columns                                                                        23                                                           Total column length                                                                            690 cm                                                       ______________________________________                                    

While we have shown and described particular embodiments of ourinvention, modifications and variations thereof will occur to thoseskilled in the art. We wish it to be understood therefore that theappended claims are intended to cover such modifications and variationswhich are within the true scope and spirit of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. In an improved process for effecting separation ofcomponents in a solution comprising an ionic component and a nonioniccomponent, the concentration of said ionic component ranging from about1 weight percent to about 20 weight percent, and the concentration ofsaid nonionic component ranging from about 1 weight percent to about 25weight percent, said improved process comprising the steps of:(1)maintaining three zones operatively connected to one another inhydraulic order, said hydraulic order comprising flow of later mentionedside streams from an outlet of the third zone to the inlet of the secondzone, from the outlet of the second zone to the inlet of the first zoneand from the outlet of the first zone to the inlet of the third zone,each of said zones containing a bed of ion exchange resin, said resinbeing in its hydrogen form; (2) introducing a stream of said solutioninto said inlet of said first zone; (3) simultaneously withdrawing froman outlet of said first zone, a stream of ionic component-enriched,nonionic component-depleted solution as product and introducing a sidestream of same into an inlet of said third zone; (4) simultaneouslyintroducing aqueous media, which is both substantially ioniccomponent-free and substantially nonionic component-free, into saidinlet of said third zone and withdrawing from an outlet thereof a streamof relatively nonionic component-rich, substantially ioniccomponent-depleted solution as product and introducing a side stream ofsame into an inlet of said second zone and withdrawing from an outlet ofsaid second zone an ionic component-depleted and nonioniccomponent-depleted solution and introducing a side stream of same intothe inlet of said first zone; (5) effecting a stepped change in the flowconnections for introduction and withdrawal of solutions among saidzones wherein the flow of said solutions is redirected such that:(a) thesolutions which were introduced into and withdrawn from the column, orcolumns which comprised said first zone are redirected to and from thecolumn, or columns which comprised said third zone, (b) the solutionswhich were introduced into and withdrawn from the column, or columnswhich comprised said third zone are redirected to and from the column,or columns which comprised said second zone, and (c) maintaining theflow connections of said side streams, whereby, upon effecting saidstepped change, the bed of resin which comprised said first zone becomessaid second zone, the bed of resin which comprised said second zonebecomes said third zone, and the bed of resin which comprised said thirdzone becomes said first zone and further whereby said stepped changesimulates movement of said resin in a direction from said first zonethrough said second zone and then though said third zone; and (6)thereafter intermittently effecting subsequent stepped changes in theflow connections among said zones to further simulate said movement ofsaid zones.
 2. The improved process of claim 1, wherein said first zonecomprises a plurality of subzones with each subzone containing a bed ofion exchange resin, said resin being in its hydrogen form, wherein eachsubzone is flow connected in series, one to the other, alternatelythrough inlets and outlets operatively associated therewith, wherein theinlet of the first subzone in such series is initially the inlet of saidfirst zone, wherein the outlet of the last subzone in such series isinitially the outlet of said first zone, and wherein the intermittentlyeffected subsequent stepped changes in the flow connections among saidzones simulates movement of said resin through said first zone in thedirection from the last subzone toward the first subzone and opposite tothat of fluid flow.
 3. The improved process of claim 2, wherein saidthird zone comprises a plurality of subzones with each subzonecontaining a bed of ion exchange resin, said resin being in its hydrogenform, wherein each subzone is flow connected in series, one to theother, alternately through inlets and outlets operatively associatedtherewith, wherein the inlet of the first subzone in such series isinitially the inlet of said third zone, wherein the outlet of the lastsubzone in such series is initially the outlet of said third zone, andwherein the intermittently effected subsequent stepped changes in theflow connections among said zones simulates movement of said resinthrough said first zone in the direction from the last subzone towardthe first subzone and opposite to that of fluid flow.
 4. The improvedprocess of claim 3, wherein said second zone comprises a plurality ofsubzones with each subzone containing a bed of ion exchange resin, saidresin being in its hydrogen form, wherein each subzone is flow connectedin series, one to the other, alternately through inlets and outletsoperatively associated therewith, wherein the inlet of the first subzonein such series is initially the inlet of said second zone, wherein theoutlet of the last subzone in such series is initially the outlet ofsaid second zone, and wherein the intermittently effected subsequentstepped changes in the flow connections among said zones simulatesmovement of said resin through said first zone in the direction from thelast subzone toward the first subzone and opposite to that of fluidflow.
 5. The improved process of claim 4, wherein said second zonecomprises from about 1 to about 9 subzones.
 6. The improved process ofclaim 5, wherein said inlets and said outlets of said zone and of saidsubzones are generally juxtaposed the bottommost regions and theuppermost regions, respectively, of said zones and said subzones.
 7. Theimproved process of claim 6, wherein each of said outlets of said zoneand of said subzones are operatively associated with a physical barrierhaving a peripheral configuration complementary to the cross-sectionaldimension of each said uppermost region and adapted for slidableengagement therewith for maintaining juxtaposition of said physicalbarrier with the top on the bed of resin in each such zone and subzoneto thereby substantially prevent the establishment over each said bed,of any substantial solution interface.
 8. The improved process of claim3, wherein said third zone comprises in the range of from about 2 toabout 23 subzones.
 9. The improved process of claim 8, wherein saidinlets and said outlets of said zone and of said subzones are generallyjuxtaposed the bottommost regions and the uppermost regions,respectively, of said zones and said subzones.
 10. The improved processof claim 9, wherein each of said outlets of said zone and of saidsubzones are operatively associated with a physical barrier having aperipheral configuration complementary to the cross-sectional dimensionof each said uppermost region and adapted for slidable engagementtherewith for maintaining juxtaposition of said physical barrier withthe top on the bed of resin in each such zone and subzone to therebysubstantially prevent the establishment over each said bed, of anysubstantial solution interface.
 11. The improved process of claim 2,wherein said first zone comprises from about 1 to about 14 subzones. 12.The improved process of claim 11, wherein said inlets and said outletsof said zone and of said subzones are generally juxtaposed thebottommost regions and the uppermost regions, respectively, of saidzones and said subzones.
 13. The improved process of claim 12, whereineach of said outlets of said zone and of said subzones are operativelyassociated with a physical barrier having a peripheral configurationcomplementary to the cross-sectional dimension of each said uppermostregion and adapted for slidable engagement therewith for maintainingjuxtaposition of said physical barrier with the top on the bed of resinin each such zone and subzone to thereby substantially prevent theestablishment over each said bed, of any substantial solution interface.14. The improved process of claim 1, wherein said inlets and saidoutlets of said zones are generally juxtaposed the bottommost regionsand the uppermost regions, respectively, of said zones.